In a high-frequency communications system, beam alignment needs to be performed between a base station and a terminal device, and the base station needs to traverse beams in all directions to ensure omnidirectional coverage of the high-frequency communications system. In a beam alignment process, the base station sends beam identifiers (beam IDs for short) of beams to the terminal device using the beams. After selecting some beams of the base station through measurement, the terminal device feeds back beam IDs of the selected beams to the base station, so that the base station and the terminal device can interact with each other over the beams selected by the terminal device. A relatively large quantity of beams exists within a coverage area of the base station, and the base station needs to number a huge quantity of beams. Therefore, a relatively large quantity of resources needs to be occupied for sending beam IDs.